American Standard Princeton Install

I am installing a American Standard Princeton bathtub. I removed underlayment floor in the bathroom down to the subfloor. Unfortunately the subfloor is only 1/2" thick. Also the floor joists run the same direction (length wise) as the tub. I plan to install a 3/4 plywood underlayment. Since the subfloor is only 1/2" would it be wise to install the 3/4" underlayment under the tub first for better support instead of installing the tub on the 1/2" subfloor as the instructions suggest? Would there be any problem with this or is it a good idea?

The 1/2" is more probably a nominal 5/8" (5/8" before sanded), as 1/2" ply never met US building codes. Adding another layer, keep in mind that the grain must run across the joists, not along them for maximum strength. It can be hard to screw a second layer to a thin one under it without stripping the screws out - you may need to predrill pilot holes in the first layer should you choose to add that second layer. Depending on what you're planning for the rest of the room, that thicker subfloor there may mean the tub edge will be hard to make look good.

To me, it would sort of depend on what the bottom of the tub looked like. If it had only a few small feet, I'd want more subflooring, but if it's fairly flat or has lots of support area, and based on their installation instructions saying it will work, I may not add more. Is the new tub going in the same location as the old one? If it worked, the new one should. If the tub bottom isn't flat or the tub doesn't sit level, you may want to embed it in mortar which will make it feel more substantial and spread the load out.

IT is much easier to install the floor first, then place the tub on top of it, which is the way I always do it, than to cut the flooring to fit the tub afterwards.

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And I almost never do it that way.
I prefer setting the tub first. The room gets backerboard and drywall. Painted and tiled, and last the floor.
You can do the floor first, but there are also so many ways to damage it in the construction process.

Thanks for the quick reply. Another question about the tub. American Standard suggest drain kit 1545.170 for the Princeton tub. It is a lift and turn drain that costs about $120. The front of the tub where the overflow goes is at an angle so I'm sure it would fit great. My questions is there an alternative drain kit that will work as well that is not so spendy? American Standard does make a cheaper one with the overflow on top to raise the water lever 2" but not interested in that one. Does anyone know of any alternative that would work and not empty the wallet? Thanks

I was thinking finished flooring too. Though most of the time I'm in there before the subfloor goes in too.
Tile is thick enough to hide any shimming I may need to do. Vinyl floors, not so much.
I did one tub where the floor was off 1/2" in five feet. That was one heck of a shimming job.

With new construction I never thought about shimming. On remodel, things can move, shift and sag over time. I lived in one home were I had to lift the center of the home up about 2". If you dropped a ball in the kitchen it would roll out the far doorway.
It's nice what two hydraulic jacks can do.

The American Standard drain should work fine. Though it has slip joints, and some places where I work doesn't allow them.
You can pick up a standard overflow kit that uses solvent weld joints for less then $30.00

It is not uncommon for the gasket that seals the top of the overflow to come with a tapered one to account for the angle (if you put it on right!). Also, some are plastic that have a short accordion like section to accommodate the angle.

Thanks guys for all the info, greatly appreciated. I plan on setting the tub in mortar. The tub has a waffle type bottom so this should work well. I read in another thread how it would be almost impossible to lay down a continuous bed of mortar, fairly level and set the tub in it. Instead it was suggested to put small piles of mortar down then set the tub in it. Makes sense. My question is and the I'm sure the answer will be hard to explain but how many of these little piles and how big and how deep. Size of a cup saucer? smaller? bigger? inch deep? more? less? Any info would be greatly apprecitated

Thanks Terry, can you give me an idea of how big the piles should be. Don't want to put down some mortar, set the tub in it then remove the tub because there is too much mortar and I have to remove some. Like it to be a one shot ordeal. Thanks!